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<html><head><title>XLISP defun</title>
<link rel="stylesheet" type="text/css" href="reference.css">
</head>
<body>
<a href="../start.htm">Nyquist / XLISP 2.0</a> -
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<a href="../examples/examples.htm">Examples</a> |
<a href="reference-index.htm">Reference</a>
<hr>
<h1>defun</h1>
<hr>
<p><table cellpadding="0" cellspacing="0" style="margin-left:10px"><tbody>
<tr valign="top">
<td><nobr>Type:</nobr></td>
<td><nobr> - </nobr></td>
<td width="100%"><nobr>special form (fsubr)</nobr></td>
</tr>
<tr valign="top">
<td><nobr>Source:</nobr></td>
<td><nobr> - </nobr></td>
<td width="100%"><nobr>xlcont.c</nobr></td>
</tr>
</tbody></table></p>
<h2>Syntax</h2>
<dl>
<dt>(defun <i>symbol arg-list body</i>)</dt>
<dd><i>symbol</i> - the name of the function being defined<br>
<i>arg-list</i> - a list of the formal arguments to the function of the form:<br>
<dl>
<dd>([<i>arg1</i> ... ]<br>
[<a href="lambda-keyword-optional.htm">&optional</a> <i>oarg1</i> ... ]<br>
[<a href="lambda-keyword-rest.htm">&rest</a> <i>rarg</i>]<br>
[<a href="lambda-keyword-key.htm">&key</a> ... ]<br>
[<a href="lambda-keyword-aux.htm">&aux</a> <i>aux1</i> ... ])<br></dd>
</dl>
<i>body</i> - a series of LISP forms (expressions) that are executed in order.<br>
returns - the function <i>symbol</i></dd>
</dl>
<h2>Description</h2>
<p>The 'defun' special form defines a new function or re-defines an
exisiting function. The last form in 'body' that is evaluated is the value
that is returned when the function is executed.</p>
<p>All of the 'argN' formal arguments that are defined are required to
appear in a call to the defined function.</p>
<p>If there are any <a href="lambda-keyword-optional.htm">&optional</a>
arguments defined, they will be filled in order.</p>
<p>If there is a <a href="lambda-keyword-rest.htm">&rest</a> argument
defined, and all the required formal arguments and
<a href="lambda-keyword-optional.htm">&optional</a> arguments are filled, any
and all further parameters will be passed into the function via the 'rarg'
argument. <b>Note</b> that there can be only one 'rarg' argument for
<a href="lambda-keyword-rest.htm">&rest</a>.</p>
<p>If there are insufficient parameters for any of the
<a href="lambda-keyword-optional.htm">&optional</a> or
<a href="lambda-keyword-rest.htm">&rest</a> arguments, they will contain
<a href="nil.htm">NIL</a>.</p>
<p>The <a href="lambda-keyword-aux.htm">&aux</a> variables are a mechanism
for you to define variables local to the function definition. At the end of
the function execution, these local symbols and their values are are
removed.</p>
<h2>Examples</h2>
<pre class="example">
(defun my-add <font color="#008844">; define function MY-ADD</font>
(num1 num2) <font color="#008844">; with 2 formal parameters</font>
(+ num1 num2)) <font color="#008844">; that adds the two paramters</font>
(my-add 1 2) <font color="#008844">; returns 3</font>
(defun foo <font color="#008844">; define function FOO</font>
(a b &optional c d &rest e) <font color="#008844">; with some of each argument</font>
(print a) (print b)
(print c) (print d) <font color="#008844">; print out each</font>
(print e))
(foo) <font color="#008844">; error: too few arguments</font>
(foo 1) <font color="#008844">; error: too few arguments</font>
(foo 1 2) <font color="#008844">; prints 1 2 NIL NIL NIL</font>
(foo 1 2 3) <font color="#008844">; prints 1 2 3 NIL NIL</font>
(foo 1 2 3 4) <font color="#008844">; prints 1 2 3 4 NIL</font>
(foo 1 2 3 4 5) <font color="#008844">; prints 1 2 3 4 (5)</font>
(foo 1 2 3 4 5 6 7 8 9) <font color="#008844">; prints 1 2 3 4 (5 6 7 8 9)</font>
(defun my-add <font color="#008844">; define function MY-ADD</font>
(num1 &rest num-list &aux sum) <font color="#008844">; with 1 arg, rest, 1 aux var</font>
(setq sum num1) <font color="#008844">; clear SUM</font>
(dotimes (i (length num-list) ) <font color="#008844">; loop through rest list</font>
(setq sum (+ sum (car num-list))) <font color="#008844">; add the number to sum</font>
(setq num-list (cdr num-list))) <font color="#008844">; and remove num from list</font>
sum) <font color="#008844">; return sum when finished</font>
(my-add 1 2 3 4) <font color="#008844">; returns 10</font>
(my-add 5 5 5 5 5) <font color="#008844">; returns 25</font>
</pre>
<p><b>Common Lisp:</b> Common Lisp supports an optional documentation
string as the first form in the 'body' of a
<a href="defmacro.htm">defmacro</a> or 'defun'. XLISP will accept this
string as a valid form, but it will not do anything special with it.</p>
<p>See the
<a href="../manual/xlisp-man-013.htm#defun">defun</a>
special form in the <nobr>XLISP 2.0</nobr> manual.</p>
<p><nobr> <a href="#top">Back to Top</nobr></a></p>
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